Ear defender with concha simulator

ABSTRACT

A hearing protection system with talk-through having a pair of rigid earcups enclosing a microphone, amplifier and speaker. A concha simulator, having a volume simulating that of the concha of a human ear, is acoustically coupled to the microphone, and also to the outside through an opening in the earcup. By coupling the microphone to the concha simulator, instead of directly to the outside, the acoustic response of the talk-through more accurately represents the hearing of a user.

REFERENCE TO RELATED APPLICATIONS

This application claims one or more inventions which were disclosed inProvisional Application No. 61/182,921, filed Jun. 1, 2009, entitled“Talk-Through Listening Device Channel Switching”. The benefit under 35USC §119(e) of the U.S. provisional application is hereby claimed, andthe aforementioned application is hereby incorporated herein byreference.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under SBIR Phase IIcontract N68335-06-C-0372, awarded by the US Navy. The government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of hearing protection. Moreparticularly, the invention pertains to hearing protection using anartificial ear structure.

2. Description of Related Art

FIG. 1 shows a hearing protection system with talk-through, in the formof a headset 13 worn by a user 14. The headset has a right earcup 1 anda left earcup 2, which serve to reduce the ambient noise level heard bythe user 14. Such protection systems are typically used in high-noiseenvironments such as aircraft carrier decks, factories, etc. In orderthat the user 14 retain some ability to hear what is going on aroundhim, microphones 3 and 4 feed a reduced amount of external sound to theuser 14 through amplifiers 5 and 6, which power audio transducers 7 and8. The amplifiers 5 and 6 can include various features known to the art,such as filtering, volume limiting or equalizing, etc. The audiotransducers can be speakers or piezoelectric or magnetic transducers inearplugs (wired or wireless), as is known to the art.

FIG. 2 shows a talk-through earcup of the prior art in more detail, withFIG. 6 showing a section of the earcup along the lines 6-6 of FIG. 2.The point here is that typical prior art talk-through systems use amicrophone 23 coupled to the outside of an earcup 21 through a hole ortube 20. The microphone 23 is sealed in a small chamber 24 so that thesound doesn't get into the earcup 21 volume. A resilient pad 22 sealsthe earcup around the pinna of a user's ear, as is common in mostaround-the-ear type earphones.

“Artificial ears” are used as objective measuring apparatus to measuresound levels, as for example for frequency response, sensitivity anddistortion measurements on earphones. They enable electroacousticalmeasurements on either insert earphones or headphones to be carried outunder well-defined acoustical conditions, which are of great importancefor the comparability of different designs and the reproducibility ofmeasurements.

International Telecommunications Union standard ITU-T P.57 (November2005) defines a standard for artificial ears. The geometry of Type 3.4artificial ears (“Pinna simulator—simplified”) is shown in FIG. 8/P.57of the standard (page 16).

Studies, such as “Sound transmission to and within the human ear canal”,Hammershøi and Møller, J. Acoust. Soc. Am. 100 (1) (July 1996), haveshown that recordings using a microphone in a blocked human ear canalretain the acoustic timing cues and directional dependence needed foraccurate localization. The concha geometry is needed to simulate humanear response, regarding localization, while the ear canal geometry isnot. The blocked canal recordings are frequency equalized when playedback for the user to compensate for the ear canal, speaker, microphone,amplifier, and other responses to provide the proper frequency responseat the user's ear canal.

SUMMARY OF THE INVENTION

The invention provides an improved hearing protection system withtalk-through using earcups which have microphones, amplifiers andspeakers, utilizing a structure based on a modified artificial ear.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a diagram of a hearing protection system with talk-through.

FIG. 2 shows a side view of a prior art earcup with talk-through.

FIG. 3 shows a side view of an earcup incorporating the invention in afirst embodiment.

FIG. 4 shows a side view of an earcup incorporating the invention in asecond embodiment.

FIG. 5 shows a hearing protection system worn under a helmet.

FIG. 6 shows a sectional view along the lines 6-6 of the earcup of FIG.2.

FIG. 7 shows a sectional view along the lines 7-7 of the earcup of FIG.3.

FIG. 8 shows a sectional view along the lines 8-8 of the earcup of FIG.4.

FIG. 9 shows a sectional view as in FIG. 8, with a variation in theposition of the microphone.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 5 depicts a talk-through system incorporating a helmet 51 andearcups (right earcup 1 is visible in FIG. 5, left earcup 2 being on theother side of the user's head), as shown in diagrammatic form in FIG.1.The helmet-based talk-through system can be used in conjunction withwired or wireless communications earplugs. The earcups 1 and 2 blockambient sounds while the microphones 3 and 4 and speakers 7 and 8 andamplifiers 5 and 6 restore those sounds at safe levels. The rigid earcupshell is designed to generally minimize acoustic transmission to theinside of the earcup. The speakers 7 and 8 can be in the earcups 1 and2, or in earplug (wired or wireless) worn inside the earcups. Earplugsare used with earcups when double hearing protection is needed such asin loud environments. The screen 40 (and concha simulator underneath)are preferable located where the human concha is located, underneath theearcup 1, to provide the best response. However, other concha simulatorlocations on the earcup, such as forward-facing as indicated in FIG. 4are acceptable.

The earcups 1 and 2 incorporate a significantly modified version of theartificial ears described in the International Telecommunications Unionstandard ITU-T P.57 (November 2005), in the form of a concha simulatorhaving a volume similar to that of a human ear. By coupling themicrophone to the concha simulator, instead of directly to the outside,the acoustic response of the talk-through more accurately reproduces thedirectional hearing characteristics of a user, making environmentalclues fed to the user through the talk-through system more useful.

An article by Burkhard and Sachs in the Journal of Acoustical Society ofAmerica (“Anthropometric manikin for acoustic research”, J. Acoust. Soc.Am., Vol. 58, No. 1 July 1975) states that average concha volume is 4.65cc for men and 3.94 cc for women with standard deviation of 0.76 cc formen and 0.81 cc for women. Hence, the concha simulator of the inventionis preferably approximately 4.30 cc in volume. However, adding 2standard deviations for women and 2 for men gives a possible volumerange for the concha simulator of approximately 6.17 cc to 2.32 cc. Theaverage depth of the human concha is approximately 1.29 cm, while theaverage concha breadth is 1.80 cm, according to Burkhard and Sachs. Theconcha simulator should preferably be approximately this deep as wellwith a similar breadth. The overall concha simulator length should beapproximately 1.85 cm, which is determined by dividing the concha volumeby the concha depth and length. However, various other reasonablegeometries can be used. The concha simulator should be rigid and notallow sound to penetrate into the earcup, else the user will be exposedto noise.

As shown in FIG. 5, screen 40 has been mounted over the concha region ofthe artificial ear to protect a microphone mounted within from debrisand fluids and also acts to dampen the acoustic response. This screen isnot used in the ITU artificial ear. The screen 50 can be made of metalmesh, textile, a gas-permeable membrane or other material that protectsthe microphone from debris, fluids, rain, snow, and other detrimentalmaterials to microphones. Acoustic damping material, such as foam, canalso be used in the concha bowel of the artificial ear to dampen theacoustic response.

FIG. 3 shows a basic embodiment of the invention, with FIG. 7 being asectional view along lines 7-7 in FIG. 3. It will be understood that theamplifier and transducer details are omitted from FIGS. 7-9, as suchdetails are not necessary to an understanding of the invention, and canbe any design as known to the art.

The opening is no longer a small hole, as shown at 20 in prior art FIG.2, but a large opening 30 with an associated volume. This volume 30forms the concha simulator, and, as discussed above, is preferablybetween 6.17 cc to 2.32 cc to simulate the general size of a humanconcha. The microphone 23 is sealed in a small chamber 24 and directedthrough an opening 31 into the volume 30 so that it measures the soundpressure level (SPL) in the volume 30.

FIG. 4 shows another embodiment of the invention, with FIG. 8 being asectional view along lines 8-8 of FIG. 4. The embodiment shown in theseFIGS. 4 and 8 builds on the embodiment of FIGS. 3 and 7. There is ascreen 40 on the outside of the concha simulator 42 to protect agas-permeable membrane 41, located directly behind it. The screen 40keeps objects and fingers from poking a hole through the membrane 41.The screen 40 can be made of metal mesh, plastic mesh or slots or othermaterials. The membrane 41 can be made of expanded PTFE material,PET-nonwoven material, polyester, cellulose, nylon or cloth, or othermaterials that are gas-permeable but help to keep out dust, debris,and/or liquid. The material used should not affect the acoustic responseappreciably or else substantial electrical equalization is needed.

Acoustic foam 43 is preferably placed in the volume of the conchasimulator 42 to dampen acoustic resonances. The microphone 23 is sealedin a small chamber 24, but is coupled to the concha simulator 42 using ahorn-shaped tube 44. The horn-shaped tube 44 can be used to acousticallyamplify sounds above 1 kHz if desired, with the length andcross-sectional area of the tubing and flaring of the horn determiningthe acoustic amplification. The relationship between a length ofstraight tubing and resonance with a microphone mounted at the end isapproximately wavelength =34,300/(4×frequency). For example, using astraight tube of length 1.72 cm will boost the frequency response atapproximately 5,000 Hz. The relationship between a length of horn-shapedtubing and amplification frequency is more complicated, but can be foundin many acoustics books.

It is advantageous to use a relatively soft material for the tubing sothat the microphone is vibration isolated from the rigid earcup.However, the tubing must be stiff enough that sound doesn't propagatethrough the walls of the tubing and into the earcup volume.

Alternatively, as shown in FIG. 9, the microphone 23 could be mountedinside the concha simulator 42.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

What is claimed is:
 1. A hearing protection system with talk-through,comprising a pair of earcups, each earcup comprising: a) a rigid earcupshell; b) a concha simulator within the earcup shell, comprising avolume between 2.32 cc and 6.17 cc simulating a volume of a concha of ahuman ear, coupled to an opening in the rigid earcup shell; c) amicrophone acoustically coupled to the concha simulator; d) an amplifiercoupled to the microphone; and e) an audio transducer coupled to theamplifier to generate sound in a user's ear canal.
 2. The hearingprotection system of claim 1, in which the microphone is inside theconcha simulator.
 3. The hearing protection system of claim 1, in whichthe microphone is outside the concha simulator, acoustically coupled tothe concha simulator through a tube.
 4. The hearing protection system ofclaim 3, in which the tube is flexible.
 5. The hearing protection systemof claim 3, in which the tube is horn-shaped.
 6. The hearing protectionsystem of claim 1, further comprising a screen on an outside of theconcha simulator, over the opening in the earcup shell.
 7. The hearingprotection system of claim 1, further comprising a gas-permeablemembrane inside the opening of the earcup shell.
 8. The hearingprotection system of claim 7, in which the membrane is made of amaterial selected from a group consisting of expanded PTFE material,PET-nonwoven material, polyester, cellulose, nylon and cloth.
 9. Thehearing protection system of claim 1, in which the concha simulatorcontains acoustic foam.
 10. The hearing protection system of claim 1, inwhich the volume of the concha simulator is approximately 4.30 cc.